pgsql: Fix build break for out of tree (vpath) builds, induced by recent

Log Message:
-----------
Fix build break for out of tree (vpath) builds, induced by recent zic
changes.

Modified Files:
--------------
pgsql/src/timezone:
Makefile (r1.18 -> r1.19)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/timezone/Makefile.diff?r1=1.18&r2=1.19)